GFCI devices are designed to trip in response to the detection of a ground fault condition at an alternating current (AC) load. Generally, the ground fault condition results when a person or object comes into contact with the line side of the AC load and an earth ground at the same time, a situation which can result in serious injury.
GFCI devices interrupt a circuit path, typically at an AC receptacle, in response to the detection of a ground fault condition at an AC load. Ground fault circuit interrupters are used in utility power applications to protect against leakage currents that flow through ground rather than back through the source's neutral line. They are commonly found in residential settings where the utility power is used to operate household appliances. In operation, a GFCI type device supplies electricity to an exterior circuit and opens an outlet circuit when a ground fault occurs in the exterior circuit, i.e., when a portion of a circuit that is plugged into the outlet becomes grounded. GFCI devices commonly include a differential current transformer, control circuit, and a circuit breaker device. Typically, a GFCI device detects this condition by using a sensing transformer or wire coil to detect an imbalance between the currents flowing in the hot and neutral conductors of the AC supply, as will occur when some of the current on the line side is being diverted to ground. A ground fault condition happens when the current is diverted to the ground through another path, such as a human body, that results in an imbalance between the currents flowing in the phase and neutral conductors. When such an imbalance is detected, a circuit breaker within the ground fault circuit interrupter is immediately tripped to an open condition, thereby opening both sides of the AC line and removing all power from the AC load.
GFCI devices may be connected to fuse boxes or circuit breaker panels to provide central protection for the AC wiring throughout a commercial or residential structure. More commonly, however, GFCI devices are incorporated into electrical receptacles that are designed for installation at various locations within a building. This type of receptacle includes test and reset pushbuttons and a lamp or light-emitting diode (LED) indicating that the circuit is operating normally. When a ground fault occurs in the protected circuit, or when the test button is depressed, the GFCI device trips and an internal circuit breaker opens both sides of the AC line. The tripping of the circuit breaker causes the reset button to pop out and the LED to be extinguished, providing a visual indication that a ground fault has occurred. To reset the GFCI device, the reset button is depressed in order to close and latch the circuit breaker, and this also causes the LED to illuminate once again.
Some electrical receptacles have apertures in their rear faces for receiving a plug terminating a plurality of wires, as disclosed in U.S. Pat. No. 4,842,551 to Heimann. The wires terminated by the plug are connected to the existing wires in any suitable manner, such as by a clamp receptacle or a wire nut. Thus, an electrician is not required to connect the plug to the receptacle. However, providing a GFCI device with such a plug results in a large and obtrusive device, particularly in view of the plug wires extending perpendicularly with respect to a rear surface of the electrical receptacle. Accordingly, a need exists for an electrical receptacle, such as a GFCI device, having a plug that snaps into an aperture in the rear surface of the receptacle, thereby providing a receptacle and plug having a low profile.